Recently, analysis to be carried out using ultraviolet light has been practiced widely in the field of, for instance, bioanalysis, particularly DNA analysis. A method in which DNA analysis is carried out accurately by determining ultraviolet ray absorption relative to a wavelength of 260 nm is disclosed in JP2002-171988 A.
In such a bioanalysis, an organic solvent such as, for example, isooctane may be used in some cases. Accordingly, materials that are not dissolved in organic solvents are required to be used for the analytical devices.
Conventionally, synthetic resin such as polystyrene generally is used as a material for the above-mentioned analytical devices. Such synthetic resin, however, does not have sufficient resistance to organic solvents. But then, when the resistance to organic solvents is improved, the ultraviolet ray transmittance of the synthetic resin tends to decrease. Accordingly, an inorganic glass composition tends to be used widely as the material for the analytical devices.
Examples of the glass having both a high resistance to organic solvents and a high transmittance for ultraviolet rays, especially ultraviolet rays having a wavelength around the range of 250 to 260 nm, include silica glass. In addition, as the glass having the above-mentioned properties, UV transmitting glass is disclosed in JP 64(1989)-79035 A and glass for a sterilizing lamp is disclosed in JP 2(1990)-252636 A. Additionally, as the glass having a high transmittance for ultraviolet rays having a wavelength around 300 nm, glass for a near-ultraviolet fluorescent lamp is disclosed in JP 61(1986)-270234 A.
The above-mentioned glass having the high ultraviolet ray transmittance, however, has the following problem.
Since the silica glass has a very high glass transition temperature and a very high softening temperature, the forming process of the silica glass by heating and softening is very difficult. Therefore, when the analytical devices described above are made using the silica glass, they are too expensive. In addition, since the silica glass has a considerably lower thermal expansion coefficient, the silica glass cannot be fusion bonded with such as commercial soda-lime silica glass that is available at a low price in producing the analytical devices described above.
The UV transmitting glass disclosed in JP 64(1989)-79035 A includes 15 to 18 wt % boron oxides as an essential component. When a silica glass composition includes alkali metal oxides, the ultraviolet ray transmittance decreases by generation of nonbridging oxygen. When the boron oxide is superadded to the glass composition, the nonbridging oxygen generated binds to the boron and the nonbridging oxygen does not stay in the glass composition. It follows that the glass composition has a high ultraviolet ray transmittance.
However, there is a problem in that boron oxide tends to vaporize from a glass melt. When boron oxide or boron compound vaporizes from a glass melt surface in melting glass, a composition of glass in the vicinity of the glass melt surface may be different from that of glass in the part other than the glass melt surface, and cords may occur in glass articles. Further, the boron oxide or boron compound volatilized erodes material such as a refractory of a melting furnace. When the refractory, etc. are eroded, there is a risk not only that the lifetime of the melting furnace is shortened but also that the ultraviolet ray transmittance of the glass composition deteriorates due to mixing of the eroded refractory into the glass melt.
The glass for a sterilizing lamp described in JP 2(1990)-252636 A includes 11 to 20 wt % of BaO+SrO. Barium is designated as one of type I designated chemical substances in the enforcement ordinance under the law of “Law concerning Reporting, etc. of Releases to the Environment of Specific Chemical Substances and Promoting Improvements in Their Management”. Therefore, it is not preferable that the glass composition includes boron oxide from the standpoint in which the trouble on environmental preservation is prevented beforehand. The analytical devices made of glass containing SrO become expensive because SrO is an expansive substance.
The healthy ray fluorescent lamp described in JP 61(1986)-270234 A has a transmittance of about 40% or more relative to a wavelength in the range of 280 to 320 nm. The glass, however, cannot be used as a material for analytical devices that are used with ultraviolet rays having a wavelength in the range of 250 to 260 nm. This is because the glass does not transmit ultraviolet rays having a wavelength in the range of shorter than 270 nm.